Discus playing possum?

[Mac6737]

This morning one of my nine adult discus was absolutely motionless, head down in some plants, with no discernible gill movement. Figuring this fish was deceased, I went to get a net. When I returned a minute or so later, there he was, swimming around, looking absolutely normal.

I've kept (and bred) discus for years, but have never seen this before. Has anyone else?

Thanks.